1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly to a PCMO thin film, and associated deposition processes, with bipolar switching characteristics for use in Resistance Random Access Memory (RRAM) applications.
2. Description of the Related Art
Perovskite materials such as Pr1-xCaxMnO3 (PCMO) show reversible resistive switching properties that can be used for low power, low operation voltage, high-speed, high-density memory applications. Nano-sized PCMO materials are known to exhibit mono-polar switching properties, while crystallized PCMO materials shows bi-polar switching properties. However, PCMO thin films are also known to exhibit poor endurance properties.
A perfectly uniform electric pulse induced resistance variation (EPIR) material memory resistor can only be programmed to a high resistance state using a relatively large amplitude narrow pulse, and reset to a low resistance state using a wide electrical pulse. However, high voltage pulses may degrade the electrical properties of the memory resistor. Further, to protect against spikes in the power supply and fluctuating supply voltages, it is often desirable to program the RRAM memory using opposite polarity (bipolar) narrow pulses to write and reset the resistance of the memory resistors.
Various methods, such as tailoring the crystalline structure and oxygen content distribution, have been proposed to create a stable material with bipolar switching characteristics. Bipolar switching can be achieved in PCMO films where there are large differences in crystalline structure. However, such a structure is difficult to scale for very thin film, small size memory devices. Likewise, bipolar switching characteristics are observed if a PCMO film is made with a higher oxygen content in the upper portion of the memory thin film, than in the lower portion. This result can be achieved easily using an annealing process, for example. However, oxygen is mobile in RRAM materials such as PCMO. Therefore, there is a reliability issue related to oxygen migration if the temperature of the device is raised in subsequent device fabrication processes or during circuit operation.
It would be advantageous if reliable, low cost, easy to scale PCMO film process could be developed that produced a PCMO film with bipolar switching characteristics.